1. Field of the Invention
The present invention relates generally to apparatus for blending viscous liquids with particulate solids, and more particularly to apparatus for blending hot asphaltic materials with ground rubber.
2. Description of the Prior Art
Currently there are considerable applications for blends of asphaltic material and ground rubber. Examples of such uses are stress absorbing pavement layers or membranes, either on top of or between other pavement layers; waterproof membranes for lakes, reservoirs and ground areas requiring stabilization and elastomeric coatings for roofs. The asphalt/rubber blends have considerably different properties than asphalt alone. In addition to have greater resiliance, the blends typically have superior low temperature and strength characteristics. Furthermore, since the rubber used is usually ground or pulverized reclaimed vehicle tires, use of asphalt/rubber blends also provides an environmentally acceptable means for disposing of scrap tires.
Numerous problems have heretofore been encountered in blending asphalt with rubber to form a relatively homogeneous slurry. Because the ground rubber is lighter in weight than the asphalt with which it is blended, the rubber tends to stay on or float to the top of slurry during blending operation. Consequently, comparatively long blending times have typically been required to produce a homogenous asphalt/rubber mixture with known blending apparatus. Besides limiting the rates at which the blends can be produced, long blending time at high temperatures, such as about 400.degree. F., required to maintain the asphalt in a fluid state tend to devulcanize the rubber. This devulcanization results in release from the rubber of liquid petroleum products which typically soften the resulting asphalt product. For such reasons, rapid blending of the asphalt and rubber is highly desirable.
In the past, blending of asphalt with rubber has typically been by a batch process wherein comparatively large quantities of asphalt and rubber are mixed together in a large tank resembling a concrete mixer. Problems arise with such large batch mixing, however, if the use of the asphalt/rubber blend is delayed, such as may be a result of unfavorable weather conditions or equipment breakdown. When long delays do occur, the entire batch of rubberized asphalt may be ruined due to the abovementioned rubber devulcanization at high temperature.
Continuous flow blending of the asphalt and rubber is, as a result, much preferred over batch blending. However, the problem has been that the prior art apparatus are inadequate to provide sufficiently high blending rates to satisfy many commonly encountered job conditions and requirements. When continuous blend processing is excessively slow, as it heretofore has generally been, men and other equipment may be idled, thereby reducing efficiency and increasing job costs. Attempts to speed up the operation of known continuous flow blending apparatus have typically resulted in nonhomogeneous asphalt/rubber blends and/or a failure to adequately wet all of the rubber with asphalt, with a resulting reduction in the mechanical strength and integrity of the applied membranes or coatings.
Also, different jobs have different blending requirements, such as requiring different ratios of asphalt or asphaltic material to ground rubber. The need to use different mix ratios may result from use of varied asphaltic materials and/or from different strength, temperature or resiliency requirements for the resulting rubberized asphalt. Consequently, the ability to accurately vary asphalt/rubber blend ratios over comparatively wide ranges is highly desirable. However, accurately variable mixing ratios have not heretofore been readily obtainable with the prior art apparatus due, at least in part, to use of electrically driven supply pumps or material transfer devices which cannot provide the necessary wide range of speed control.
Furthermore, it is believed that provision has not heretofore been made for directly indicating the blend ratio, so as to enable improved blending control and readily blend ratio verification.
Accordingly, it is a primary object of this invention to provide an improved apparatus for continuously blending viscous liquids, such as asphalt, with particulate solids, such as ground rubber, so as to avoid the aforementioned deficiencies of the prior art apparatus.
Another object of the invention is to provide an apparatus capable of accurately blending viscous liquids and particulate solids to produce slurries having a wide variety of liquid to solids ratios.
Still another object of the invention is to provide an apparatus which can economically and effectively produce on a continuous basis a blend of hot asphalt and rubber of a selected liquid to solid ratio while allowing the continuous monitoring of the blending ratio to verify that the desired ratio is employed.
A further object of this invention is provide a relatively compact apparatus for continuously blending viscous liquids and solids at high rates such that said apparatus can be vehicle-mounted if desired.
Additional object, advantages and features of the invention will become apparent to those skilled in the art from the following description when taken in conjunction with the accompanying drawing.